Quinoid Compounds and Their Use in Semiconducting Matrix Materials, Electronic and Optoelectronic Structural Elements

ABSTRACT

The invention relates to quinoid compounds and their use in semiconductive matrix materials, electronic and optoelectronic structural elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 12/667,440, filed Mar. 15, 2010, which is a national phase entry of PCT Patent Application No. PCT/DE2008/001080, filed Jul. 2, 2008, which claims foreign priority to German Patent Application No. 102007031220.4, filed Jul. 4, 2007. Each of these applications is incorporated herein by reference.

The invention relates to quinoid compounds and their use as dopant for the doping of an organic semiconductive matrix material, as charge injection layer, as hole blocker layer, as electrode material, as transport material itself, as storage material in electronic and/or optoelectronic structural elements, as well as to an organic semiconductive material and electronic or optoelectric structural elements.

The changing of organic semiconductors by doping as regards their electrical properties, especially their electrical conductivity, as is also the case for inorganic semiconductors such as silicon semiconductors, is known. Here, an elevation of the conductivity, which is quite low at first, as well as, depending on the type of dopant used, a change in the Fermi level of the semiconductor is achieved by generating charge carriers in the matrix material. A doping results here in an elevation of the conductivity of charge transport layers, which reduces ohmic losses, and in an improved transition of the charge carriers between contacts and organic layer. Inorganic dopants such as alkali metals (e.g., cesium) or Lewis acids (e.g., FeCl₃, SbCl₅) are usually disadvantageous in organic matrix materials due to their high coefficient of diffusion since the function and stability of the electronic structural elements is adversely affected, see D. Oeter, Ch. Ziegler, W. Göpel Synthetic Metals (1993) 61 147-50; Y. Yamamoto et al. (1965) 2015; J. Kido et al. Jpn J. Appl. Phys. 41 (2002) L358-60. In addition, the latter dopants have such a high vapor pressure that a technical use is very questionable. Moreover, the reduction potentials of these compounds is often too low for doping technically really interesting hole conductor materials. In addition, the extremely aggressive reaction behavior of these dopants makes a technical use difficult.

The basic object of the present invention is to provide compounds that can be used as dopant, as charge injection layer, as hole blocker layer, as electrode material, as transport material itself or as storage material and can overcome the disadvantages of the state of the art. The compounds should preferably have a sufficiently high reduction potential, have no disturbing influences on the matrix material and provide an effective elevation of the charge carrier number in the matrix material and be relatively simple to handle.

Further objects of the present invention consist in indicating possibilities for using these compounds as well as providing organic semiconductive materials and electronic or optoelectronic structural elements in which the disclosed compounds can be used.

For example, dianions and radical anions that are materially the same compounds as the quinoid compounds but are merely present in another oxidation state should be understood as derivatives of the quinoid compounds.

The first object is solved by the quinoid compounds according to claim 1. The further objects are solved by the subject matters of the further independent claims and preferred embodiments are given in the subclaims.

It was surprisingly determined that the quinoid compounds in accordance with the invention yield a significantly stronger and/or more stable dopant than previously known acceptor compounds, during which the novel quinoid structures are used in neutral form as p-dopant opposite an organic semi-conductive matrix material.

In particular, the conductivity of charge transport layers is significantly elevated when using the compounds in accordance with the invention and/or the transition of the charge carriers between the contacts and organic layer is significantly improved in applications as electronic structural element. Without being limited by this conception, it is assumed that CT complexes are formed in the use in accordance with the invention of the quinoid structures in a doped layer, especially by the transfer of at least one electron from the particular surrounding material. Also, cations of the matrix material are formed that can move on the matrix material. In this manner the matrix material gains a conductivity that is elevated in comparison to the conductivity of the non-doped matrix material. Conductivities of non-doped matrix materials are as a rule <10⁻⁸ S/cm, especially frequently <10⁻¹⁰ S/cm. Care should be taken here that the matrix materials have a sufficiently high purity. Such purities can be achieved with traditional methods, for example, gradient sublimation. The conductivity of such matrix material can be elevated by doping to greater than 10⁻⁸ S/cm, frequently >10⁻⁵ S/cm. This is true in particular for matrix materials that have an oxidation potential of greater than −0.5 V vs. Fc/Fc⁺, preferably greater than 0 V vs. Fc/Fc⁺, especially greater than +0.2 V vs. Fc/Fc⁺. The indication Fc/Fc⁺ refers to a redox pair ferrocene/ferrocenium that is used as reference in an electrochemical determination of potential, for example, cyclovoltammetry.

The quinoid compounds can also be used as hole injection layer. Thus, for example, a layer structure of anode/acceptor/hole transporter can be produced. The hole transporter can be a pure layer or a mixed layer. In particular, the hole transporter can also be doped with an acceptor. The anode can be, for example, ITO. The acceptor layer can be, for example, 0.5-100 nm thick.

It was furthermore established in accordance with the invention that the described quinoid compounds can also be used as injection layer in electronic structural components, preferably between an electrode and a semiconductor layer, that can also be doped, or also as blocker layer, preferably between emitter- and transport layer in electronic structural elements. The compounds used in accordance with the invention have a surprisingly high stability relative to their reactivity with the atmosphere.

Doping

Among others, phthalocyanine complexes, for example, Zn (ZnPc), Cu (CuPc), Ni (NiPc) or other metals can be used as p-dopable matrix material, and the phthalocyanine ligand can also be substituted. Other metal complexes of naphtocyanines and porphyrines can optionally also be used. Furthermore, arylated or heteroarylated amines or benzidine derivatives can also be used as matrix material, which can be substituted or unsubstituted, for example TPD, a-NPD, TDATA, especially also spiro-linked ones such as, e.g., spiro TTB. In particular, a-NPD and spiro TTB can be used as matrix material.

In addition to polyaromatic hydrocarbons heteroaromatics such as in particular imidazole, thiophene, thiazole derivatives, heterotriphenylenes but also others can also be used as matrix material, optionally also dimeric, oligomeric or polymeric heteroaromatics. The heteroaromatics are preferably substituted, especially aryl-substituted, for example phenyl- or naphthyl-substituted. They can also be present as spiro compounds.

It is understood that the named matrix materials can also be used in the frame-work of the invention mixed with each other or with other materials. It is understood that suitable other organic matrix materials can also be used that have semiconductive properties.

Doping Concentration

The dopant is preferably present in a doping concentration of ≦1:1 relative to the matrix molecule or to the monomeric unit of a polymeric matrix molecule, preferably in a doping concentration of 1:2 or less, especially preferably 1:5 or less or 1:10 or less. The doping concentration can be in the range of 1:1 to 1:100,000, especially in the range of 1:5 to 10,000 or 1:10 to 1,000, for example in the range of 1:10 to 1:100 or 1:25 to 1:50 without being limited to the above.

Carrying Out the Doping

The doping of the particular matrix material with the compounds to be used in accordance with the invention can take place by one or a combination of the following processes:

Mixed evaporation in the vacuum with a source for the matrix material and one for the dopant.

Sequential depositing of the matrix material and of the p-dopant on a substrate with subsequent diffusing in of the dopant, especially by thermal treatment.

Doping of a matrix layer by a solution of p-dopant with subsequent evaporation of the solvent, especially by thermal treatment.

Surface doping of a matrix material layer by a layer of dopant applied on the surface.

Production of a solution of matrix molecules and dopant and subsequent production of a layer of this solution by conventional methods such as, for example, evaporation of the solvent or centrifuging.

The doping can optionally also take place in such a manner that the dopant is evaporated out of a precursor compound that releases the dopant during heating and/or irradiation. For example, a carbonyl compound, dinitrogen compound or the like can be used as precursor compound that spits off CO, nitrogen or the like during the release of the dopant and other suitable precursors can also be used such as, for example, salts, e.g., halogenides or the like. The heat necessary for evaporation can be substantially provided by an irradiation and it can also be radiated in a targeted manner into certain bands of the compounds or precursors or compound complexes to be evaporated such as charge transfer complexes in order to facilitate the evaporation of the compounds by dissociation of the complexes, e.g., by transfer into excited states. However, the complex can in particular also be sufficiently stable for evaporating under the given conditions in a non-dissociated manner or for being applied onto the substrate. It is understood that other suitable processes can also be used to carry out the doping.

Thus, p-doped layers of organic semiconductors can be produced in this manner that can be used in multiple ways.

Semi-Conductive Layer

Semiconductive layers can be produced by the quinoid structures used in accordance with the invention that are optionally designed rather linearly such as, e.g., conductivity paths, contacts or the like. The quinoid structures can be used here as p-dopants together with another compound that can function as matrix material and the doping ratio can be 1:1 or less. The dopant used can also be present in higher amounts relative to the particular other compound or component so that the ratio of dopant: compound can be in the ratio of >1:1, for example, in the ratio of ≧2:1, ≧5:1, ≧10:1 or ≧20:1 or higher. The particular other component can be one such as can be used a matrix material in the case of the production of doped layers, without being limited to it. The dopant used can optionally also be present substantially in pure form, for example, as pure layer.

The area containing a dopant or consisting substantially or completely of it can be brought in contact in an electrically current-conducting manner with an organic semiconductive material and/or with an inorganic semiconductive material, for example, arranged on such a substrate.

In particular the quinoid structures are preferably used in accordance with the invention as p-dopants, e.g., in a ratio of ≦1:1 or ≦1:2. For example, when using ZnPc, spiro TTB or a-NPD as matrix semiconductive layers with conductivities at room temperature in the range of 10⁻⁵ S/cm or higher, for example, 10⁻³ S/cm or higher, for example, 10⁻² S/cm can be achieved by the electron-withdrawing compounds used in accordance with the invention as p-dopants. When using phthalocyanine zinc as matrix a conductivity of greater than 10⁻⁸ S/cm was achieved, for example 10⁻⁶ S/cm. On the other hand, the conductivity of non-doped phthalocyanine zinc is maximally 10⁻¹⁰ S/cm.

It is understood that the layer or the structure with the dopants can contain one or more different quinoid structures.

Electronic Structural Element

When using the described compounds to produce p-doped organic semiconductor materials that can be arranged in particular in the form of layers or electronic conduction paths a plurality of electronic structural elements or equipment containing the latter can be produced with a p-doped organic semi-conductor layer. In the sense of the invention the concept “electronic structural elements” also comprises optoelectronic structural elements. The electronic properties of an electronically functionally active area of the structural element such as its electrical conductivity, light-emitting properties or the like can be advantageously changed by using the described compounds. Thus, the conductivity of the doped layers can be improved and/or the improvement of the charge carrier injection of contacts into the doped layer can be achieved.

The invention comprises in particular organic light-emitting diodes (OLED), organic solar cells, field effect transistors, organic diodes, in particular those with a high rectification ratio such as 10³-10⁷, preferably 10⁴-10⁷ or 10⁵-10⁷, and organic field effect transistors that were produced by the electron-withdrawing quinoid structures. An electron-withdrawing group or acceptor group or electron-withdrawing structures should be understood in such a manner according to the present invention that they have a stronger electron-withdrawing effect than hydrogen. The concept “electron-withdrawing aryl- and heteroaryl groups” denotes aromatics and/or heteroaromatics that are electron-poor according to the invention and have a lower electron density than benzene.

In the electronic structural element a p-doped layer based on an organic matrix material can be present, for example, in the following layer structures, in which the base materials or matrix materials of the individual layers are preferably organic:

p-i-n: p-doped semiconductor-intrinsic semiconductor-n-doped semiconductor,

n-i-p: n-doped semiconductor-intrinsic semiconductor-p-doped semiconductor.

“i” is again a non-doped layer, “p” is a p-doped layer. The contact materials are hole-injecting here and on the p side, for example, a layer or a contact of ITO or Au can be provided, or electron-injecting, and on the n side a layer or a contact of ITO, Al or Ag can be provided.

In the above structures the i layer can also be omitted if necessary, in which case layer sequences with p-n or n-p transitions can be obtained.

However, the use of the described compounds is not limited to the above-cited exemplary embodiments, in particular, the layer structures can be supplemented or modified by the introduction of additional suitable layers. In particular, OLEDs with such layer sequences, in particular with pin structure or with a structure inverse to it, can be built up with the described compounds.

In particular, organic diodes of the metal-insulator-p-doped semiconductor type (min) or also optionally of the pin type can be produced with the aid of the described p-dopants, for example on the basis of phthalocyanine zinc. These diodes display a rectification ratio (rectification ratio, relative to the current flow in the direction of passage in contrast to the current flow in the reverse direction of the structural part) of 10⁵ and higher. Furthermore, electronic structural elements with p-n transitions can be produced using the cited compounds, in which the same semiconductor material is used for the p- and the n-doped side (homo p-n transition).

However, the compounds in accordance with the invention can also be used in the electronic structural elements in layers, conductivity paths, point contacts or the like if they predominate relative to another component, for example, as injection layer in pure or substantially pure form.

Further objects and advantages of the present invention will now be described in an illustrative manner using the following examples that are to be considered solely as illustrative and not as limiting the scope of the invention.

Preparation of the Quinoid Compounds

The quinoid compounds in accordance with the invention can be synthesized from the appropriate dihydro compounds by oxidation according to known processes, which dihydro compounds can be prepared from electron-poor aromatics or heteroaromatics by nucleophilic substitution of CH-acidic compounds, see L. Brucsis, K. Friedrich Chem. Ber. 109 (1976) 2469-74; S. Yamaguchi et al. Bull. Chem. Soc. Jpn. 62 (1989) 3036-7; E. L. Martin U.S. Pat. No. 3,558,671, as is shown here using the example of the hexafluorobenzene a and a cyanotetrafluorobenzene acetonitrile compound b in the following equation.

A protective group on the CH-acidic reactants such as, e.g., alkyl, benzyl, trialkylsilyl or thioalkoxy can be advantageous for the second substitution.

EXAMPLES OF SYNTHESIS Dihydro Compounds Synthesis of 4,4′-Decafluorodibenzhydryenl-2,3,5,6,2′,3′,5′,6′-octafluorobiphenylene

2 eq dipentafluorophenyl-t-butylmethane in a little glyme are slowly compounded under ice cooling and protective gas to a suspension of 2 eq sodium hydride in glyme. After the addition has been concluded the mixture is agitated 30 min longer at room temperature. 1 eq decafluorobiphenyl is rapidly added and the mixture heated 3 h at 60° C. After cooling off, the mixture is precipitated with water and washed with a little methanol and ether. The obtained product is converted in an atmosphere of protective gas for a few minutes in boiling diphenylether under splitting off of butane into the yellow-orangish product, which can be removed by suction after cooling off. Fp.: >250° C.

Synthesis of 3,6 bis[1-cyano-1-(4-cyano-tetrafluorophenyl)-methylene]-2,5-difluoro-phenyl-1,4-dicarbonitrile

2.5 mmol tetrafluoroterephthalonitrile and 5.1 mmol NaH were suspended in 50 ml dimethoxyethylene under argon. 6.0 mmol (1.28 g) 2-t-butyl-4′-cyanotetrafluorophenylacetonitrile in 5 ml dimethoxyethylene were dropped at 5° C. into this mixture. After 30 h agitation at room temperature the mixture was poured onto 200 ml ice water and acidified with hydrochloric acid. The purple-colored solid obtained was filtered off and dried in the vacuum. The product was purified by recrystallization from a suitable solvent and butane subsequently split off in diphenylether at 250° C. After cooling off, ether was added and the mixture adjusted cold. The precipitated product was removed by suction and dried in the vacuum. (yield 1.55 g). ESE-MS analysis (negative detection, direct inlet from a solution in MeOH/0.5 mM NH4OAc): m/z=587 [M-H]⁻, 293 [M-2H]²⁻.

Synthesis of the Quinoid Compounds (Oxidation) Synthesis von 3,6-bis[1-cyano-1-(4-cyano-phenyl)-methylidene]-2,5-difluoro-cyclohexa-1,4-diene-1,4-dicarbonitrile

The corresponding dihydro compound was compounded without further purification to the complete solution with glacial acetic acid and a mixture of nitric acid and hydrobromic acid cooled to 0° C. added. After the conclusion of the addition the mixture was agitated still at room temperature, compounded with water until the start of the precipitation of a solid and agitated further at room temperature. The orange-colored solid was removed by suction, washed with water and dried in the vacuum (yield over all stages 76%). DI-MS (EI): m/z=586 [M]⁺. ¹⁹F-NMR (CD₃CN): δ=−100.5 (m, 2F), −127.7 (m, 4F), −131.6 (m, 4F) ppm.

APPLICATION EXAMPLES FOR THE DOPING

An extremely electron-poor and electron-withdrawing quinoid compound is provided very cleanly.

The electron-poor quinoid compound placed in a receiver is evaporated simultaneously with the matrix material. According to the exemplary embodiment the matrix material is phthalocyanine zinc, spiro-TTB or a-NDP. The p-dopant and the matrix material can be evaporated in such a manner that the layer precipitated on a substrate in a vacuum evaporation system has a doping ratio of p-dopant to matrix material of 1:10.

The particular layer of the organic semi-conductor material doped with the p-dopant is applied on an ITO layer (indium tin oxide) arranged on a glass substrate. After the application of the p-doped organic semiconductor layer a metal cathode is applied, for example, by vapor-depositing a suitable metal in order to produce an organic light-emitting diode. It is understood that the organic light-emitting diode can also have a so-called inverted layer construction in which the layer sequence is: glass substrate-metal cathode-p-doped organic layer-transparent conductive cover layer (for example ITO). It is understood that further layers can be provided between the individual cited layers depending on the application.

Doping with_3,6-bis[1-cyano-1-(4-cyano-phenyl)-methylidene]-2,5-difluoro-cyclohexa-1,4-diene-1,4-dicarbonitrile

The doping performance was checked by Co evaporation of 3,6-bis[1-cyano-1-(4-cyano-phenyl)-methylidene]-2,5-difluoro-cyclohexa-1,4-diene-1,4-dinitrile (5 mol %) with spiro TTB and measuring the conductivity of the mixed layer obtained. A conductivity of the doped layer of 1.8×10⁻⁴ Scm⁻¹ was found.

The features of the invention disclosed in the above description and in the claims can be essential individually as well as in any combination for the realization of the invention in its different embodiments. 

1. A quinoid compound or derivative thereof, wherein the quinoid compound is selected from the group consisting of:

wherein: R¹-R⁸ are independently selected from halogen, CN, NO₂, COR, perhalogenated or partially halogenated C₁-C₁₀ alkyl groups, substituted or unsubstituted electron-withdrawing aryl-, or substituted or unsubstituted electron-withdrawing heteroaryl groups; R¹⁰-R¹⁵ are independently selected from hydrogen, halogen, CN, NO₂, COR, C₁-C₁₀ alkyl, C₁-C₁₀ alkoxy, substituted or unsubstituted electron-withdrawing aryl-, or substituted or unsubstituted electron-withdrawing heteroaryl groups; X, X₁, Y, and Y₁ are independently selected from:

wherein: Z is selected from halogen, NO₂, NO, CF₃, COR, or SO₂R; R is selected from substituted or unsubstituted C₁-C₁₀ alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; Ar is an acceptor-substituted and halogenated aromatic hydrocarbon; and Hetaryl is an acceptor-substituted and/or halogenated, electron-withdrawing aromatic heterocyclic compound.
 2. The quinoid compounds according to claim 1, wherein R¹-R⁸ are selected independently from fluorine or perfluorinated C₁-C₁₀ alkyl groups.
 3. The quinoid compounds according to claim 1, wherein R¹⁰-R¹⁵ are selected independently from perfluorinated C₁-C₁₀ alkyl groups.
 4. The quinoid compounds according to claim 1, wherein the acceptor substituent of Ar is a nitrile group, and the other positions of Ar are halogenated with fluorine atoms.
 5. The quinoid compounds according to claim 1, wherein Ar is a polycyclic compound or biaryl.
 6. The quinoid compounds according to claim 1, wherein the acceptor-substituent of Hetaryl is a nitrile group.
 7. The quinoid compounds according to claim 1, wherein Hetaryl is a polycyclic compound.
 8. The quinoid compounds according to claim 1, wherein Hetaryl is completely halogenated by fluorine.
 9. An electronic or optoelectronic structural element comprising a dopant for doping an organic semiconductive matrix material, a charge injection layer, a hole blocker layer, an electrode material, a transport material, or a storage material, wherein the dopant for doping an organic semiconductive matrix material, the charge injection layer, the hole blocker layer, the electrode material, the transport material, or the storage material comprises a quinoid compound or derivative thereof, wherein the quinoid compound is selected from the group consisting of:

wherein: R¹-R⁸ are independently selected from halogen, CN, NO₂, COR, perhalogenated or partially halogenated C₁-C₁₀ alkyl groups, substituted or unsubstituted electron-withdrawing aryl-, or substituted or unsubstituted electron-withdrawing heteroaryl groups; R¹⁰-R¹⁵ are independently selected from hydrogen, halogen, CN, NO₂, COR, C₁-C₁₀ alkyl, C₁-C₁₀ alkoxy, substituted or unsubstituted electron-withdrawing aryl-, or substituted or unsubstituted electron-withdrawing heteroaryl groups; X, X₁, Y, and Y₁ are independently selected from:

wherein: Z is selected from halogen, NO₂, NO, CF₃, COR, or SO₂R; R is selected from substituted or unsubstituted C₁-C₁₀ alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; Ar is an acceptor-substituted and halogenated aromatic hydrocarbon; and Hetaryl is an acceptor-substituted and/or halogenated, electron-withdrawing aromatic heterocyclic compound.
 10. The electronic or optoelectronic structural element of claim 9, comprising an organic semiconductive material comprising an organic matrix compound and a dopant, wherein the dopant comprises at least one of the quinoid compounds or derivatives thereof.
 11. The electronic or optoelectronic structural element according to claim 10, wherein the molar doping ratio of dopant to matrix molecule or the doping ratio of dopant to monomeric units of a polymeric matrix molecule is between 20:1 and 1:100000.
 12. The electronic or optoelectronic structural element according to claim 9, comprising an electronically functionally active area, wherein the electronically active area comprises at least one of the quinoid compounds or derivatives thereof.
 13. The electronic or optoelectronic structural element according to claim 12, wherein the electronically active area comprises an organic semiconductive matrix material doped with at least one dopant for changing the electronic properties of the semiconductive material, wherein the dopant comprises at least one of the quinoid compounds or derivatives thereof.
 14. The electronic or optoelectronic structural element according to claim 12, wherein the element is an organic light-emitting diode, a photovoltaic cell, an organic solar cell, an organic diode, or an organic field effect transistor. 